1. Field of the Invention
The present invention relates to an ultrasonic motor and the like.
2. Description of the Background Art
Ultrasonic motors having an ultrasonic vibrator that uses a vibration of a piezoelectric element have been used. The ultrasonic vibrator has such distinctive features that it is not affected by magnetism, is small in size, has a high torque, has a high response speed and is at rest when it is not energized. These and other features are different from those of an electromagnetic motor. Therefore, the ultrasonic motor is a potential element particularly for an autofocus drive mechanism of a small camera lens and the like.
The piezoelectric element used in the ultrasonic vibrator is formed of a brittle material such as ceramic so that it has a poor shock resistance. It has been known that wear due to driving occurs in contact portions of the ultrasonic vibrator and an external driver such as a rotor, resulting in deterioration of performance of the ultrasonic motor. For example, Japanese Patent Laying-Open No. 2005-073341 has proposed an ultrasonic vibrator having a contact portion that is made of a material such as stainless steel (SUS) or the like having a high shock resistance and a high wear resistance, and is fixed to a vibration plate.
FIGS. 18 and 19 show examples of the above ultrasonic vibrator that has a high shock resistance and a high wear resistance, and particularly shows contact portions in ultrasonic vibrators 900 and 904 disclosed in Japanese Patent Laying-Open No. 2005-073341.
Contact portion 901 in ultrasonic vibrator 900 shown in FIG. 18 has an arc-shaped outer periphery, which is in contact with a semicircular inner peripheral surface of a notch formed in a vibration plate 903. Contact portion 901 is attached to vibration plate 903 by an adhesive or the like.
According to the above structure, adhesivity of the adhesive must be larger than a pulling force in a longitudinal direction of the vibration plate, i.e., in an x-axis direction in FIG. 18. In this case, contact portion 901 is disengaged from the vibration plate when the pulling force in the x-direction larger than the above adhesivity is applied between contact portion 901 and the vibration plate during the attaching operation or driving of ultrasonic vibrator 900.
A vibration plate 905 of an ultrasonic vibrator 904 shown in FIG. 19 has a notch having an arc-shaped inner peripheral surface, and is provided at the notch with a projection 906. A contact portion 907 is provided with an engagement portion 908. Projection 906 is engaged with engagement portion 908 to prevent disengagement of contact portion 907 from vibration plate 905.
According to the above structures, however, each of contact portion 907 and vibration plate 905 has the arc-shaped portion and the linear portion in a mixed fashion, which complicates working thereof. Further, as shown in FIG. 19, a space is present between vibration plate 905 and contact portion 907 in ultrasonic vibrator 904. This space prevents efficient transmission of the vibration of vibration plate 905 to contact portion 907, resulting in loss of an output power of the ultrasonic vibrator.